One of the most widely used pieces of equipment used in a newspaper or commercial printing operation is a high-speed web offset press. Generally, these offset presses have three cylinders: (1) a plate cylinder to which the plate carrying the image is secured; (2) a blanket cylinder covered with a rubber sheet or blanket and a tangential engagement with the plate to receive from the plate the inked portions of the image; and (3) an impression cylinder in contact with the blanket cylinder. The paper passes between the latter two cylinders at the nip between said cylinders to receive the printed image from the blanket cylinder. When printing on both sides, the blanket cylinder of one printing cylinder combination may serve as the impression cylinder of the opposing combination.
In an offset press running at speeds of 15,000 to 60,000 impressions per hour and printing on, for example, 32 pound newsprint stock, the accumulation of lint from the paper stock, and a combination of ink and water on the blanket soon causes a deleterious build-up of foreign matter. This build-up tends to distort the image area and printed unwanted images on the paper. When the point is reached where the reproductive quality falls below the acceptable standard, an inferior printed product is produced and wastage inevitably occurs.
In the past, one solution to the problem of foreign matter or dirt buildup has been for an operator to periodically stop the press when the build-up has reached a critical stage, and manually, with a cleaning solvent and rag, wash the blanket of each printing couple. The problem with manually washing the blanket is that the rag leaves streaks due to inconsistent solvent application and unequal pressure. Also, valuable minutes of daily production are wasted while the press is idle.
Generally, this problem has been dealt with by stop gap measures. For example, the printing press is operated at a slow speed and a solvent soaked cleaning rag is held against the blanket while the press is operating. However, this is a highly dangerous method because an operator is likely to get his hand caught, especially while maneuvering the rag in the vicinity of the pressure nip between the cylinders. In addition, the equipment itself can be damaged by the loose rag becoming entangled in the press. Furthermore, because web newsprint continues through the printing press, relatively large amount of spoiled paper stock results.
In order to improve the efficiency of operation of the offset press and to help protect the operator from injury, several types of automatic blanket cleaning systems have been proposed for incorporation in the presses. For example, in one type of automatic system, a cleaning unit is installed on the underside of each printing unit to automatically apply a fine mist spray of cleaning solvent to the blanket or printing surface. This solvent causes the build-up on each blanket cylinder to be broken up and then carried away on a sheet of newsprint. However, this unit, as is obvious, also causes a substantial amount of paper to be wasted as the blanket is being cleaned. Further, this prior art is not effective against the ground-in dirt since there is no scrubbing action.
In another type of automatic system, a roller shaped cleaning tool is applied against the cylindrical surface of the blanket cylinder to be cleaned. A plurality of spray nozzles in proximity to the cylindrical surface apply an atmosphere of atomized cleaning liquid against the surface. Because of the induced atomization, the "misting" problem is paramount and an enclosure must be provided. A vacuum system draws off the atmosphere containing the cleaning solvent and some entrapped dirt. A separate spray nozzle is provided to apply a cleaning liquid to the rotating cleaning tool, which is, in turn, squeezed by a roller.
This automatic cleaning apparatus has the disadvantage of requiring a number of separate spray nozzles. The original cost of the hardware and the relatively large amount of solvent needed make the system very expensive to install and operate. Further, the cleaning solvent tends to be applied to the cylinder and cleaning tool unevenly and without being accompanied by immediate scrubbing and wiping action on the cylindrical surface adjacent the pressure nip. Streaks are produced on the cylinder as the cylinder is rotated because of this uneven distribution of the solvent and drying of the solvent by the large volume of air sucked into the enclosure by the vacuum system. In addition, since the squeeze roller pushes on the roller, the tendency is for the dirt trapped in the roller to be worked up to the surface and reapplied to the cylinder. The roller tools are inconvenient to remove and require a substantial amount of time and effort on the part of the operator.
Finally, in the past the economic pressure to develop an improved automatic blanket cleaning system has not been as great as it is today. Since the operator had to stop the press to splice the newsprint web anyway, most companies have opted not to purchase the previous automatic systems but to stick with the manual cleaning. Today, with automatic web splicing equipment being installed on virtually all of the presses, an efficient and inexpensive automatic cleaning system is needed more than ever.